Among its numerous physiological functions, the epidermis possesses the function of constituting a barrier that is at once biological, physical and chemical against the invasion of the organism by microorganisms.
The properties of the epidermis as a physical barrier are, notably, associated with its structural organization.
Thus, the epidermis is conventionally divided into a basal layer of keratinocytes constituting the stratum germinativum of the epidermis, the stratum spinosum constituted of several layers of polyhedral cells and finally a number of upper layers called cornified layers (or stratum corneum), constituted of keratinocytes at the final stage of their differentiation, called corneocytes.
The chemical barrier properties of the epidermis notably depend on the release, at the surface of the epidermis, of numerous antimicrobial proteins such as cathelicidins, the serine protease inhibitor antileukoprotease, dermcidin or proteins of the β-defensin family.
Numerous disorders or pathologies of the skin or of the scalp can result from dysfunction of the epidermal cellular structural organization, or from a defect in the chemical barrier function of the epidermis, such as dry skin, psoriasis, atopic dermatitis, ichthyosis, hyperkeratosis, inflammatory reactions resulting from microbial infections, or dandruff conditions.
To date, there are only a few biological markers for efficiently and accurately determining the condition of the epidermis, and notably for relating a disorder of the skin or of the scalp to a dysfunction of its physiological functions.
There is thus a need for biological markers that allow precise characterization of the condition of the epidermis.
There is also a need for a biological marker that could be used reliably in a method of diagnosis of a disorder of the skin or of the scalp.
There is also a need to identify new cosmetic or therapeutic targets in the epidermis.
There is also a need for new tools for screening molecules capable of exerting a cosmetic or therapeutic action on the epidermis or on keratinous materials in general. In the sense of the invention, the term “epidermis” will designate both the skin and the scalp.
There is also a need for new cosmetic or therapeutic compositions that can be used for the treatment of disorders of the skin or of the scalp resulting from the aforementioned dysfunction.
The present invention aims to meet all these needs.